To produce color filters by conventional means, for example, black matrices are formed between red (R), green (G) and blue (B) pixels so as to improve their display contrast. Such known means include, for example, a method of forming a film of metal such as chromium to obtain black matrices and a method of using a photosensitive resin containing a dispersion of a light-shielding pigment or the like. According to these methods, the R, G and B pixels are arranged to partly overlap the black matrices so as to prevent the formation of transparent portions caused, for example, by misalignment.
To form black matrices of a film of metal Such as chromium according to the former method, a metallic film is formed on a substrate by metallic vapor deposition, and then the film is patterned by photolithographic etching using a photoresist. According to the latter method, a photosensitive resin layer containing a dispersion of a light-shielding pigment or the like is formed on a substrate by coating or printing, and then the coated substrate is subjected to a process comprising pattern-wise exposure and development to form black matrices.
Regarding the latter method, it is advantageous in view of reduced production costs and production steps to employ a self-alignment system, using a photosensitive resin containing a dispersion of a light-shielding pigment or the like, to form black matrices. This technique is illustrated in JP-A-62-9301 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). According to this system, a photosensitive resin layer containing a dispersion of a light-shielding black pigment, such as carbon black, or the like, is formed on a substrate having thereon R, G and B pixels. The coated substrate is then exposed to light which is applied thereto from the back surface of the substrate while the R, G and B pixels act as photo-masks, to thereby form black matrices between the pixels. The system is advantageous in that a positioning step for alignment, which, however, was indispensable in the conventional means, is not needed. Furthermore, this system, in principle, does not give rise to any transparent portions.
According to the self-alignment system, however, the photosensitive light-shielding material provided on the B pixels reacts with light passing through the B pixels having a large light transmittance at about 400 nm. This causes fog due to the light-shielding material remaining on the B pixels. In order to avoid this problem, it was necessary to reduce the amount of light applied to the back surface of the substrate for exposure, while controlling the amount of this light so as not to fog the B pixels. In this case, however, since a sufficient amount of light could not be applied to the back surface of the substrate for satisfactory exposure, the desired light-shielding film was partly etched by development with the result that the optical density of the light-shielding film was lowered.
In order to prevent the above-described fogging of B pixels caused by exposure from the back surface of the substrate, JP-A-6-59119 proposed a method of exposing the substrate from its back surface, via an optical filter capable of cutting off light having a wavelength of 400 nm or longer, to thereby form a light-shielding film having a high optical density. However, the method is disadvantageous in that the optical filter is thermally weak. That is, when the optical filter is set up between a sample and a light source, the optical filter expand on account of the heat of the light source to be damaged.